Transcript Enterprise Internets

Frame Relay, ATM
and VPN
Packet-Switched Services
 Offered

X.25
 Old,

by Carriers
slow, and not sufficiently cheaper than frame relay
Frame Relay
 Speeds
in main range of user demand
 Attractive prices
 Dominates the market today

ATM
 High
speeds and costs
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X.25 Packet-Switched Data Networks

Oldest packet switched network service (1970s)

Low speed (maximum around 64 kbps)
 Mature:
easy to implement

Uses PVCs

Reliable service, so latency in transmission

Mostly replaced by Frame Relay
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Frame Relay Packet-Switched Data
Networks

Software upgrade to X.25 switches

Uses PVCs

Unreliable, so much faster on same switches

Good speed range: 56 kbps - 40 Mbps: Meets
most corporate needs (most under 2 Mbps)

Priced aggressively to kill leased lines
(succeeding)

Best-selling packet switched network service
See more here.
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ATM (Asynchronous Transfer Mode)
 Offers
 622
very high speeds
Mbps, 2.5 Gbps to 40 Gbps
 Connection-oriented
 Quality
(PVCs), unreliable
of Service (QOS) guarantees critical
traffic
 Minimize
latency (delays)
 Inherent reliability (low loss rate)
 Technical
details beyond this course
Building more bandwidth than needed
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ATM

Speeds are beyond most corporate needs today

High costs

Seen as the next generation
 But
Frame Relay keeps increasing in speed in low
Mbps range where market demand is highest

Used by providers

e.g. AT&T, to support both ATM and Frame Relay for
customers
See AT&T ATM pricing
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Pricing Packet Switched Services

Customer Premises Equipment

Access Line to Point of Presence
 Port
Speed

Per PVC Price

Distance and Traffic Volume
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Customer Premises Equipment

Access Device
 Has
link to internal system (often a LAN)
 Has CSU/DSU to put internal traffic into format for
Frame Relay transmission
 In Frame Relay, called Frame Relay Access Device
(FRADS)
Access Device
Access Line
to Network
LAN
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Modular Routers

CSU/DSUs are removable expansion boards
Modular Router
Router Switching Circuitry
Port 1
CSU/DSU
(T1)
Port 2
CSU/DSU
(56 kbps)
Port 3
CSU/DSU
(T3)
Port 4
CSU/DSU
(56 kbps)
T1 Line
56 kbps Line
T3 Line
56 kbps Line
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Elements of a Packet Switched Network
Customer
Premises
A
LEC
Switching
Office
Leased
Access Line
to POP
Leased
Access Line
to POP
POP
at LEC
Office
You need a leased access
line to the network’s
POP.
Sometimes the packet
switched network vendor
pays the cost of the
access line for you and
bundles it into your
service charges.
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Elements of a Packet Switched Network
Switched
Data
Network
Trunk
Line
Network
Switching
Office
Customer
Premises B
POP
Leased
Access Line
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Pricing of Frame Relay

Speed of the Access Line from Site to Network
 Determines
maximum transmission rate to the network
 Often
called the Port Speed (not in the book)
 Often
the most important price determinant
 Must
be fast enough for needs
See Frame Relay over DSL -- a price issue
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Pricing of Frame Relay

In Some Frame Relay networks, two speeds
 Committed
Information Rate (pretty much guaranteed)
 Available
Bit Rate (like flying standby) for bursts. Not
guaranteed.
 Price
depends both on CIR and ABR
 Access
line speed must be fast enough for ABR
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Pricing of Frame Relay

Additional price per PVC
 Usually
small compared to the access line charge
 One access line can multiplex all PVCs to/from site
 PVCs share access line speed
PVC1
Site
PVC2
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Calculations

Situation
 You
have four sites
 You want any one to be able to reach any other

Questions
 How
many PVCs do you need?
 How many access lines do you need?
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Calculations

PVCs
 If
you have N sites, there are N(N-1)/2 possible
connections
 In this case, you would have 4(3)/2 or 6 possible
connections
 Some vendors count this as 6 PVCs, others as 12 PVCs

Access Lines
 You
would need four access lines (one for each site)
 Each will multiplex 3 PVCs
 Must be fast enough for the needs of communication
with the three other sites
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Pricing of Frame Relay

May Depend on Distance
 But
often a flat monthly rate throughout the carrier’s
service area

May Depend on Traffic
 But
often a flat monthly rate based only on the speed of
the access line
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Leased Lines vs. Packet-Switched Data
Networks

Leased Lines
 Point-to-point,
inexpensive for thick routes
 Inflexible: must be established ahead of time

Packet Switched Networks
 Also
must be established ahead of time for PVCs
 Competitor for leased line networks
 Priced aggressively
 Carrier does all the management
 Killing the leased line business
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Circuit-Switched vs. Packet-Switched
Services

Circuit Switched Networks (ISDN, Switched 56)
 Any-to-any connectivity by dialing number
 Highest speed is ISDN: 64 kbps to 128 kbps

Packet Switched Networks (X.25, Frame Relay, ATM)
 PVCs make them primarily competitors to leased lines
 Megabit to gigabit speeds
 SVCs may provide any-to-any flexibility in the future
 IP services, MPLS, ATM trends
Note: more MPLS details
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Virtual Private Network
1.
Site-to-Site
Tunnel
Internet
VPN Server
VPN Server
Corporate
Site B
Corporate
Site A
Extranet
2. Remote
Customer PC
(or site)
Remote
Access for
Intranet
3. Remote
Corporate PC
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VPN advantage

Virtual Private Network (VPN)
 Transmission
over the Internet with added security
 Some analysts include transmission over a PSDN with
added security

Why VPNs?
 PSDNs
are not interconnected
 Only good for internal corporate communication
 But Internet reaches almost all sites in all firms
 Low transmission cost per bit transmitted
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VPN issues

VPN Problems
 Latency
and Sound Quality
 Internet can be congested
 Creates latency, reduces sound quality
 Use a single ISP as for VoIP (voice over IP)
 Security
 PPTP
for remote access is popular
 IPsec for site-to-site transmission is popular
 New IP services (see MCI offerings)
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ISP-Based PPTP Remote Access VPN
 Remote Access
VPNs
 User
dials into a remote access server (RAS)
 RAS often checks with RADIUS server for user
identification information. Allows or rejects connection
Unsecure TCP
Control Channel
Local
Access
Secure Tunnel
RADIUS
Server
PPTP
RAS
Corporate
Site A
Internet
ISP
PPTP
Access
Concentrator
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VPN and PPTP

Point-to-Point Tunneling Protocol
 Available
in Windows since Windows 95
 No need for added software on clients
 Provided by many ISPs
 PPTP access concentrator at ISP access point
 Some security limitations
 No security between user site and ISP
 No message-by-message authentication of user
 Uses unprotected TCP control channel
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IPsec alternatives

IP Security (IPsec)
 Tunnel
mode: sets up a secure tunnel between IPsec
servers at two sites
 No security within sites
 No need to install IPsec software on stations
 Transfer
mode: set up secure connection between two
end hosts
 Protected even on internal networks
 Must install IPsec software on stations
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IPsec in Tunnel Mode
Local
Network
IPsec
Server
Tunnel
Mode
IPsec
Local
Server
Network
Secure
Tunnel
No Security
In Site Network
Tunnel Only
Between Sites
Hosts Need No
Extra Software
No Security
In Site Network
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IPsec in Transfer Mode
Local
Network
IPsec
Server
Transfer
Mode
IPsec
Local
Server
Network
Secure
Tunnel
Security
In Site Network
End-to-End (Host-to-Host)
Tunnel
Hosts Need IPsec Software
Security
In Site Network
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Security at the internet layer

IP Security (IPsec)
 At
internet layer, so protects information at higher
layers
 Transparent:
upper layer processes do not have to be
modified
HTTP
Protected
SMTP
TCP
FTP
SNMP
UDP
Internet Layer with IPsec Protection
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Common IPsec configuration

IP Security (IPsec)
 Security
associations:
 Governed
by corporate policies
Party A
Party B
List of
Allowable
Security
Associations
List of
Allowable
Security
Associations
IPsec Policy Server
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